viii BLOOD-STEEAM: MOVEMENT IN VESSELS 257 



of the blood column that traverses the section of the said artery 

 in the time-unit, usually 1". It can easily be calculated when the 

 sectional area of the artery and the amount of blood that traverses 

 it in the time-unit are known. 



The first to attempt the exact determination of this point was 

 Volkmaun (1846). His method was adopted by Ludwig (1867) 

 who perfected Volkmann's haemodromometer. His instrument (the 

 Strorniihr'} permitted the repetition on the same animal, for an 

 indefinite number of times, of the determination of the mean 

 velocity of the circulation, so that its variations with changes of 

 experimental conditions can be investigated. 



Ludwig'sStromuhr or haemo- 

 dromometer (Fig. 99) consists of 

 two glass receivers of equal 

 capacity (A, B), which com- 

 municate above by a U-bend, 

 in the centre of which there is 

 a tube opening to the exterior. 

 By means of this aperture the 

 bulb A can be filled with oil, 

 and bulb B with physiological 

 saline, after which the aperture 

 is closed by a stop-cock. The 

 cannula a (which communicates 

 with the bulb A) is then con- 

 nected with the central end of 

 the artery, and the cannula b 

 (which communicates with the 

 bulb B) with its distal end. As 

 soon as the blond reaches the 

 stromuhr, it penetrates A and 

 drives the oil into B, when the 

 salt solution contained in the 



latter is driven into the peripheral part of the artery. When the 

 blood has completely filled the bulb A, the two receivers which 

 are reversible upon the metal plate c are changed by a rapid half- 

 turn, so that A is now in connection with the cannula b, and B 

 with cannula a. The bulb containing oil is now again filled with 

 blood, and the oil once more driven into the bulb A, and so on. 

 If the number of turns in a given time are counted, then with 

 known capacity of the receivers it is easy to calculate the total 

 quantity of blood flowing in that time through the artery, from 

 which the quantity passing per second can be calculated. 



Tigerstedt modified Ludwig's Stromuhr by substituting for the 

 two receivers a single, accurately calibrated glass cylinder, along 

 which runs a hollow metal ball. The pressure of the blood drives 

 this ball from one end of the cylinder to the other : so soon as 



VOL. I s 



FIG. 09. Lud wig's haemodromometer or Stromuhr. 

 A, B, Glass bulbs of equal capacity ; a, 1>, can- 

 nulae to be connected with central and periph- 

 eral trunks of artery ; c, metal plate fixed on a 

 support, on which the air-tight metal disc in 

 which the two receivers end can rotate. 



